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R. J. Lucas, M. A. Cameron, A. E. Allen, T. M. Brown; Rod Visual Responses in the Absence of Rod -Transducin. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1665.
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Photoreception is mediated by outer-retinal rod and cone photoreceptors, and melanopsin-expressing retinal ganglion cells. Gnat1-/- Cng3a-/- Opn4-/- (triple knock-out) mice lack critical elements of the phototransduction cascades associated with each of these mechanisms, via specific ablation of the rod transducin alpha-subunit, cone cyclic nucleotide gated channel, and melanopsin gene. Although assumed blind, these mice retain a small, transient pupillary light reflex. This led us to investigate whether other visual responses are also retained in this genotype and, if so, what photoreceptor drives them.
Flash ERGs were recorded from wild type and triple knock-out mice under dark adapted conditions and against a rod-saturating background light (2.6 log10 µW.cm-2). Light-dependent changes in spike-firing rate were assessed via multi-electrode recordings in the pretectum and thalamus of anaesthetised triple knock-out mice.
We report a low amplitude but highly reproducible flash ERG in triple knock-out mice, indicating relatively widespread light-evoked activity in retinal neurons. This response originates in the outer retina, and has a spectral sensitivity matching that of rod opsin. In vivo recordings of neurons within retino-recipient areas also reveal light-evoked increases in firing rate.
Here we have identified an array of visual responses downstream of an α-transducin independent mechanism of phototransduction that is active in rod photoreceptors.
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